All serum samples from 12 guinea pigs infected as weanlings via different routes of inoculation contained Viral Capsul Antigen (VCA) serum antibodies to Epstein Barr Virus (EBV) with titers ranging from 1:10 to 1:40 over a period of one year. No Early Antigen (EA) serum antibodies have been detected during this period. Fifteen animals inoculated intrautero or in the bone marrow with EBV have shown VCA serum antibodies (1:20 to 1:80) and, more important, nine revealed EA antibody to EBV, with titers ranging from 1:10 to 1:80 as judged by indirect immunofluorescence. Sera obtained from four of seven animals injected intrautero with Herpes saimiri (HVS) had antibodies of both VCA (1:20 to 1:80) and EA (1:10 to 1:20).